1. Field of the Invention
A toroidal-type continuously variable transmission according to the present invention is used as a transmission unit constituting an automatic transmission apparatus for a vehicle or as a transmission for adjusting the operating speeds of various kinds of industrial machines such as a pump.
2. Description of the Related Art
As an example of a transmission unit which constitutes a transmission for a vehicle, there is known a toroidal-type continuously variable transmission and the toroidal-type continuously variable transmission is conventionally enforced in part of the vehicle industry. The toroidal-type continuously variable transmission, which has been conventionally enforced in part of the vehicle industry, is a toroidal-type continuously variable transmission of a so called double cavity type which transmits power from an input part thereof to an output part thereof by using two systems arranged in parallel to each other. This type of toroidal-type continuously variable transmission is disclosed in many publications such as the U.S. Pat. No. 5,033,322 publication, U.S. Pat. No. 5,569,112 publication, and U.S. Pat. No. 5,651,750 and is thus conventionally known, while the basic structure of this toroidal-type continuously variable transmission will be described below with reference to FIG. 3.
According to the toroidal-type continuously variable transmission shown in FIG. 3, an input side disk 2a is supported on the periphery of the near-to-base-end portion of the middle portion of an input rotary shaft 1 (in FIG. 3, the left-shifted portion) and a second input side disk 2b is supported on the periphery of the near-to-front-end portion of the middle portion of the input rotary shaft 1 (in FIG. 3, the right-shifted portion). The input side disk 2a and the second input side disk 2b are respectively supported through their associated ball splines 4, 4 and in such a manner that their respective input side inner surfaces 3, 3 respectively formed as toroidal curved surfaces are opposed to each other. Therefore, the two input side disks 2a, 2b are respectively supported on the periphery of the input rotary shaft 1 in such a manner that they can be shifted in the axial direction of the input rotary shaft 1 and can be rotated synchronously with the input rotary shaft 1.
Also, between the base end portion of the input rotary shaft 1 and the outer surface of the input side disk 2a, there are interposed a rolling bearing 5 and a pressing device 6 of a loading cam type. And, a cam plate 7 constituting the pressing device 6 is disposed so as to be driven or rotated by a drive shaft 8. On the other hand, between the front end portion of the input rotary shaft 1 and the outer surface of the second input side disk 2b, there are interposed a loading nut 9 and a countersunk plate spring 10 having a large elastic force.
The middle portion of the input rotary shaft 1 penetrates through a through hole 13 opened up in a partition wall portion 12 formed in the interior of a casing 11 (see FIGS. 1 and 2 which show an embodiment of the present invention) in which a toroidal-type continuously variable transmission is stored. On the inside diameter side of the through hole 13, there is rotatably supported a cylindrical-shaped output cylinder 28 by a pair of rolling bearings 14, 14, while an output gear 15 is fixedly secured to the outer peripheral surface of the middle portion of the output cylinder 28. Also, two output side disks 16a, 16b are respectively supported by spline engagement on such portions of the two end portions of the output cylinder 28 that are projected from the two outer surfaces of the partition wall portion 12 in such a manner that they can be rotated synchronously with the output cylinder 28. In this state, the output side inner surfaces 17, 17 of the respective output side disks 16a, 16b respectively formed as toroidal curved surfaces are respectively opposed to the input side inner surfaces 3, 3. Also, between the outer peripheral surface of the middle portion of the input rotary shaft 1 and such portions of the respective inner surfaces of the two output side disks 16a, 16b that are projected from the end edges of the output cylinder 28, there are respectively interposed needle roller bearings 18, 18; and thus, while supporting loads to be applied to the respective output side disks 16a, 16b, the needle roller bearings 18, 18 allow the output side disks 16a, 16b not only to rotate with respect to the input rotary shaft 1 but also to shift in the axial direction of the input rotary shaft 1 with respect to the input rotary shaft 1.
Also, in each of such intermediate portions (cavities) between the input side and output side inner surfaces 3, 17 that are situated in the periphery of the input rotary shaft 1, there are interposed a plurality of (generally, two or three) power rollers 19, 19. The power rollers 19, 19 are respectively structured such that the peripheral surfaces 29, 29 thereof to be contacted with the input side and output side inner surfaces 3, 17 are formed as spherically-shaped convex surfaces. The power rollers 19, 19 are respectively supported on the inner surface portions of their associated trunnions 20, 20 corresponding to support members as set forth in the appended claims of the present specification in such a manner that they can be rotated and can be swung and shifted slightly by displacement shafts 21, 21, radial needle roller bearings 22, 22, thrust ball bearings 23, 23, and thrust needle roller bearings 24, 24. That is, each of the displacement shafts 21, 21 is an eccentric shaft in which its base half section and its front half section are set eccentric to each other; and, the base half sections of the displacement shafts 21 are respectively supported on the middle portions of their associated trunnions 20, 20 by another radial needle roller bearings (which are not shown) in such a manner that they can be swung and shifted.
The power rollers 19, 19 are respectively rotatably supported on the front half sections of the thus-structured displacement shafts 21, 21 by the radial needle roller bearings 22, 22 and thrust ball bearings 23, 23. Also, the above radial needle roller bearings (not shown) and thrust needle roller bearings 24, 24 permit the shifting movements of the respective power rollers 19, 19 with respect to the axial direction of the input rotary shaft 1 that could be caused by the elastic deformation of the respective composing members.
Further, the trunnions 20, 20 respectively support their associated pivot shafts, which are disposed on the two end portions (in FIG. 3, the end portions situated in the front and back direction) of the trunnions 20, on support plates 25a, 25b (see FIGS. 1 and 2 which show first and second embodiments of the present invention) installed on the interior of the casing 11 in such a manner that the pivot shafts can be swung as well as can be shifted in the axial directions thereof. That is, the trunnions 20, 20 are supported in such a manner that not only they can be shifted clockwise and counterclockwise in FIG. 3 but also they can be shifted in the axial directions of the pivot shafts (in FIG. 3, in the front and back direction; and, in FIGS. 1 and 2, in the vertical direction) by actuators (not shown).
To operate the above-structured toroidal-type continuously variable transmission, the input side disk 2a may be driven or rotated by the drive shaft 8 through the pressing device 6. This pressing device 6 drives or rotates the input side disk 2a while generating propulsive power going in the axial direction of the input rotary shaft 1; and thus, the pair of input side disks 2a, 2b including the above input side disk 2a are rotated synchronously with each other while they are being pressed toward their respective output side disks 16a, 16b. As a result of this, the rotational movements of the input side disks 2a, 2b are transmitted through the power rollers 19, 19 to the output side disks 16a, 16b respectively, thereby rotating the output gear 15 which is coupled to the output side disks 16a, 16b through the output cylinder 28.
When the toroidal-type continuously variable transmission is in operation, the propulsive power generated by the pressing device 6 secures surface pressures between the respective contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input side and output side inner surfaces 3, 17. Also, the surface pressures increase as the power (torque) to be transmitted from the drive shaft 8 to the output gear 15 increases. Therefore, there can be obtained a good transmission efficiency regardless of variations in the torque. Also, even in case where the torque to be transmitted is 0 or very small, a preload spring 26 disposed on the inside diameter side of the pressing device 6 can secure the surface pressures in the respective contact portions to a certain degree. Due to this, the torque transmission in the respective contact portions can be executed smoothly without causing excessive slippage just after the toroidal-type continuously variable transmission is put into operation.
To change a transmission ratio between the drive shaft 8 and output gear 15, the trunnions 20, 20 may be shifted in the front and back direction in FIG. 3 by the irrespective actuators (not shown). In this case, the trunnions 20, 20 disposed in the upper half section of FIG. 3 and trunnions 20, 20 in the lower half section thereof are shifted by the same quantities in the mutually opposite directions. The shifting movements of the trunnions 20, 20 change the directions of the forces that are applied to the tangential directions of the contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input side and output side inner surfaces 3, 17. And, due to such change in these tangential-direction forces, the trunnions 20, 20 are respectively swung about their associated pivot shafts disposed on the two end portions thereof. These swinging movements of the trunnions 20, 20 change the positions of the contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input side and output side inner surfaces 3, 17 with respect to the diameter directions of the two inner surfaces 3, 17. The more these contact portions change outwardly in the diameter direction of the input side inner surface 3 and inwardly in the diameter direction of the output side inner surface 17, the more the transmission ratio changes to the speed increasing side. On the other hand, the more these contact portions change inwardly in the diameter direction of the input side inner surface 3 and outwardly in the diameter direction of the output side inner surface 17, the more the transmission ratio changes to the speed reducing side.
In the case of the conventional structure shown in FIG. 3, since not only the output gear 15 but also the pair of rolling bearings 14, 14 are interposed between the respective outer surfaces 27, 27 of the pair of output side disks 16a, 16b, the distance D27 between the two outer surfaces 27, 27 is large. This increases the axial-direction dimension of the toroidal-type continuously variable transmission, which increases the size and weight of the toroidal-type continuously variable transmission. Such increased size and weight is caused not only by the increase in the distance D27 but also by an increase in the axial-direction thickness of the output side disks 16a, 16b. The reason for this is as follows.
In the speed reducing state of the toroidal-type continuously variable transmission shown in FIG. 3, the peripheral surfaces 29, 29 of the power rollers 19, 19 press against the output side inner surfaces 17, 17 of the output side disks 16a, 16b while they are contacted with the near-to-outside-diameter portions of the output side inner surfaces 17, 17. Due to this, a large moment about the spline engaged portion of the output cylinder 28 is applied to the output side disks 16a, 16b. In order not only to restrict variations in the transmission ratio but also to secure the durability of the output side disks 16a, 16b, it is necessary to restrict the elastic deformation of the output side disks 16a, 16b. And, in order to restrict such elastic deformation, it is necessary to increase the axial-direction thickness dimensions of the output side disks 16a, 16b to thereby enhance the rigidity of the output side disks 16a, 16b. Thus, in case where the axial-direction thickness dimensions of the output side disks 16a, 16b are increased for these reasons, the size of the toroidal-type continuously variable transmission is increased in the above-mentioned manner.